Blob on toilet paper after wiping..

I am on cycle day 64. My period was late last month so my doctor said to start my birth control to bring it on. I have been having cramps for a week now and cramping isn't normal for me. I also took my nuva ring out last Monday. I started spotting 2 days ago (brown in colour) but it was only very little when I wiped. Yesterday I passed a blood clot that was dark with a little bit of bright red blood. So I thought my period had finally started. I used a tampon yesterday and when I changed it there was very little on it and it was very dark. So this morning when I got up and went to the bathroom, I wiped and seen a big blob on the toilet paper. It was greyish with some blood. When I removed my tampon there was still not a whole lot on it but more this time. It was a darker red. So what I am wondering is, is it my uterine lining or a miscarriage? Anyone have any advice on what I should do or if I should do anything?

Edited to add I have take 4 pregnancy tests in these 64 days and all were negative. Not even the faintest line.